In recent years, with increasing demand for shortening the delivery time for photographic prints and improving printing productivity, there has been a tendency for printing time to be shortened by rapid development using silver halides having high silver chloride contents for high developing speed and by sensitivity improvement in photographic light-sensitive materials for printing. However, silver chloride emulsions are poor in coating solution stability. The poor stability of coating solution causes a large fluctuation in sensitivity and gradation within a lot, thus limiting lo size expansion.
Also, other problems arise in multi-layered color light-sensitive materials; for example, sensitivity and gradation differences among layers hamper the obtainment of the desired photographic performance due to imbalance in color, and unevenness in photographic characteristics within a lot results in considerable yield reduction when prints are made under predetermined exposure conditions in photo-finishing laboratorys in the case of light-sensitive materials for color printing paper because different printing results are obtained from different rolls.
To prevent such characteristics deterioration during standing of coating solution, there have been proposed a number of methods, including the method in which an azole, an azaindene compound or another known stabilizer is added, the method in which a reducing agent such as hydroquinone or sulfinic acid is added, the method using a combination of a copolymer and a brightening agent, as described in Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) No. 111629/1974, and the method in which a sensitizing dye is added to coating solution, as described in Japanese Patent O.P.I. Publication No. 7629/1983. However, none of these methods, whether used singly or in combination, could be considered satisfactory.
On the other hand, unlike the conventional 5-pyrazolone-based magenta coupler, the recently-developed 1H-pyrazolo-[1,5-b]-1,2,4-triazole-based magenta coupler offers excellent color reproduction because of the absence of undesirable absorption around 430 nm in the resulting coloring dye, but the magenta dye thus obtained is known to be poor in light fastness.
Meantime, Japanese Patent O.P.I. Publication No. 262159/1985, for instance, describes the use of a phenol or phenyl ether compound to improve light fastness; however, the obtained effect remains unsatisfactory, and further improvement is desired.
Attempts to improve light fastness have been made from the viewpoint of coupler structure as well. For example, the 1H-pyrazolo-[1,5-b]-1,2,4-triazole-based magenta couplers described in Japanese Patent O.P.I. Publication Nos. 307453/1988, 66646/1989, 161430/1990, 296241/1990, 111943/1990 and 138644/1991, all of which have a bulky substituent at 6 position, are known to be excellent in light fastness. However, the use of these couplers poses a problem of further deterioration of coating solution stability, and improvement is demanded strongly.